SUB-GENUS ACASTA. 307 



sack, which run to the opercular valves, seemed rather feeble 

 in most of the species. The penis in several species was 

 remarkably long, and in A. spongites I noticed the straight 

 projecting point at its dorsal base, as is common in Balanus. 



Affinities, 8fc. — At the commencement of the description 

 of the genus, I gave my reasons for keeping Acasta dis- 

 tinct as a sub-genus from Balanus. The species are particu- 

 larly troublesome to identify, not only from the great 

 variability of the most obvious characters, but from the very 

 close general external appearance of most of the species, and 

 the consequent necessity for cleaning and disarticulating at 

 least one specimen in every group. The shape, however, of 

 the shell and basis, and the state of their disarticulated edges, 

 whether smooth, crenated, or toothed, here offer more service- 

 able, though still very variable, characters for the identifi- 

 cation of the species, than is usual with sessile cirripedes ; 

 and this, probably, is in part due to the almost free or un- 

 attached condition of the whole shell, suspended, as it were, 

 in the midst of sponges, which they inhabit. The opercular 

 valves, on the other hand, are less serviceable than usual. 



Range, Habitats, 8fc. — The species are found all over the 

 world, excepting in the very cold latitudes.* Acasta 

 laevigata ranges from the Red Sea to the Philippines ; 

 A. spongites from the south of England and Wales to the 

 Cape of Good Hope ; and A. cyatkus from Madeira to the 

 West Indies ; most of the other species seem to have rather 

 confined ranges. The East Indian Archipelago seems to 

 be the metropolis of the genus, for here A. laevigata, 

 fenestrata,pmpurata } and sporillus, are all found. Of these 

 four species, A. purpurata lives imbedded, not in sponges, 

 but in the sponge-like bark of an Isis ; and I think it pro- 

 bable, that A. sporillus may have somewhat analogous 

 habits. The same species often lives imbedded in different 

 kinds of sponge j thus, I have seen A. Icevigata and cgathus 

 in apparently three kinds, and A. spongites in, as I believe, 

 four kinds. The genus existed during the miocene period, in 

 the Coralline Crag, under a form closely allied to A. spongites. 



* I am greatly indebted to Mr. Bowerbank for bis great kindness, in looking 

 over bis immense collection of sponges from all parts of the world, and sending 

 to me all the specimens of Acasta be could find imbedded in them. 



